Object-oriented programming languages may support inheritance, which may use an existing type to derive a new type. Derived types may inherit data and operations of super-type of the derived types; and they may overwrite existing operations or add new ones. Complex object-oriented programs may contain complex inheriting hierarchies. These hierarchies may often require that the program explicitly convert an object reference from one type to another type. This type of conversion may need run-time type checking that may be used to check whether the object is cast into an invalid target type. For most implementation of object-oriented programming languages, besides a memory to store fields of an object, each object may have an object header to provide basic services of object-oriented programming, such as class hierarchies with virtual methods, and other metadata that may be tapped into for different kinds of uses.